U.S. patent application number 12/522451 was filed with the patent office on 2010-03-04 for method and device for tightening a surgical cable.
Invention is credited to Rogier Oosterom.
Application Number | 20100057091 12/522451 |
Document ID | / |
Family ID | 38134859 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100057091 |
Kind Code |
A1 |
Oosterom; Rogier |
March 4, 2010 |
METHOD AND DEVICE FOR TIGHTENING A SURGICAL CABLE
Abstract
The invention relates to a method for tying together objects, in
particular for fixing hone parts by a surgical cable (10),
comprising the steps of laying the surgical cable, having two end
parts, around at least part of the objects to be tied together, in
particular the bone parts (40) to be fixed, bringing the two end
parts together and tying them with a connection, which is slipping
when a relatively high force is applied, exerting this relatively
high force on the end parts which allows the connection to slip,
thereby bringing the cable under a tension required for tying
together the objects, in particular for fixing the bone parts. The
invention also relates to a tensioning device (1) for exerting the
force on the surgical cable.
Inventors: |
Oosterom; Rogier; (Utrecht,
NL) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
38134859 |
Appl. No.: |
12/522451 |
Filed: |
December 13, 2007 |
PCT Filed: |
December 13, 2007 |
PCT NO: |
PCT/EP07/10958 |
371 Date: |
November 9, 2009 |
Current U.S.
Class: |
606/103 |
Current CPC
Class: |
A61B 17/823 20130101;
A61B 2017/0475 20130101; A61B 2017/0496 20130101; A61B 2017/0474
20130101; A61B 2090/064 20160201; Y10T 428/31692 20150401; A61B
17/82 20130101; A61B 2017/0477 20130101; Y10T 428/31855 20150401;
A61B 17/8869 20130101; A61B 17/8861 20130101; A61B 90/06
20160201 |
Class at
Publication: |
606/103 |
International
Class: |
A61B 17/58 20060101
A61B017/58 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2007 |
EP |
07000393.4 |
Claims
1. Method for tying together objects, in particular for fixing bone
parts by a surgical cable, comprising the steps of laying the
surgical cable, having two end parts, around at least part of the
objects to be tied together, in particular the bone parts to be
fixed, bringing the two end parts together and tying them with a
slipping connection, exerting a force on the end parts which
exceeds the slip strength of the connection, thereby bringing the
cable under a tension required for tying together the objects, in
particular for fixing the bone parts.
2. Method according to claim 1, wherein the force exerted on the
cable ends to increase compression on the objects is 2 to 10 times
higher than the force in the cable around the objects, more
preferably 4 to 5 times higher.
3. Method according to claim 1, wherein the slipping connection
comprises a knot.
4. Method according to claim 1, wherein the connection is made such
that the slip strength of the connection exceeds the average
tension required for tying together the objects, in particular for
fixing the bone parts, by 20% of the tension required.
5. Method according to claim 1, including the step of locking the
tensioned cable against the influence of forces acting counter to
the exerted force.
6. Method according to claim 5, wherein locking the tensioned cable
against the influence of forces acting counter to the exerted force
is achieved by tying at least one additional knot.
7. Method according to claim 1, wherein the cable comprises
ultrahigh molecular weight polyethylene fibers.
8. Method according to claim 1, wherein the exerted force is a
tensile force, and the force is exerted by a tensioning device.
9. Method according to claim 1, wherein the exerted force yields a
tensile stress in the end parts of at least 650 MPa.
10. A tensioning device for a surgical cable comprising: a
restraining body adapted to restrain the surgical cable to be laid
around at least part of the objects to be tied together; an
adjusting mechanism adapted to cooperate with the restraining body
to change the tensile force applied to the surgical cable; whereby
the device is adapted to allow the surgical cable to be tensioned
by the restraining body at a tension of at least 1000 N.
11. A tensioning device according to claim 10, whereby the device
and the surgical cable are adapted to allow the surgical cable to
be tensioned by the restraining body at a tension of at least 900
N, more preferably at least 1000 N, still more preferably at least
1200 N, and most preferably at least 2400 N.
12. A tensioning device according to claim 10 further comprising
measuring means for the applied tension.
13. A tensioning device according to claim 9, wherein the
restraining body comprises an adjustable frame, provided with at
least two guiding means in opposite corners of the frame, between
which means a surgical cable can be tightened, the adjusting
mechanism being adapted to change the relative distance between
said corners of the frame, thereby increasing or decreasing the
tension in the cable, if the relative distance is increased or
decreased, respectively.
14. Surgical cable prepared for application in a method according
to claim 1, or for application in the tensioning device.
Description
[0001] The invention relates to a method and device for tightening
a surgical cable around objects, in particular bone parts in order
to tie them together.
[0002] In surgery a frequent need arises to internally immobilize
bone parts that have been separated due to a trauma or in the
course of an operation and need to grow together again, or to keep
a bone part at some distance and position with respect to another
bone part or an orthopedic device such as a splint, further denoted
as fixing bone parts. In treating bone fractures fixing the
previously separated bone parts is required for at least the time
needed to allow the bones to grow together. Longer periods of time,
in many cases even years, may however also be required.
[0003] In a known surgical method, a steel cable is wrapped around
the bone parts to be fixed, brought under the required tension to
secure the parts against relative movement, e.g. under load, and
then left in place inside the body at least until the bone parts
have grown together and the bone has recovered sufficiently to take
up its proper function. The cable may also remain inside the body
permanently to avoid a further operation to remove the cable. The
cable is tensioned and fixed by guiding its ends from opposite
sides through holes in a metal block, tensioning the cable by
exerting a drawing force on the ends using a tensioning device, and
pinching the metal block such that the holes collapse and fix the
cable by a clamping force.
[0004] The use of separate fixing devices is inconvenient for a
surgeon, who has to handle these tiny devices under the pressure of
an operation. Also, devices based on pinching may not work properly
in all cases, or may loosen after some time.
[0005] The object of the present invention is therefore to provide
a method for tying together objects, in particular for fixing bone
parts by means of a surgical cable, which method does not suffer
from the above mentioned disadvantages and provides easy and secure
application of the cable.
[0006] The method of the invention thereto comprises the steps of
laying the surgical cable, having two end parts around at least
part of the objects to be tied together, in particular the bone
parts to be fixed, bringing the two end parts together and tying
them with a slipping connection, exerting a force on the end parts
which exceeds the slip strength of the connection, and thereby
bringing the cable under the tension required for tying together
the objects, in particular for fixing the bone parts.
[0007] The method can in principle be applied to any surgical cable
in which a slipping connection can be tied. A particularly suitable
cable however comprises ultrahigh molecular weight polyolefin
fibers, and ultrahigh molecular weight polyethylene fibers in
particular. Fibers of this type are notorious for their difficulty
to be fixed by knots, clamps or other means when they are under
tension. The essence of the invented method is that this drawback
is now used to advantage. In particular, by using this property, a
connection is readily provided which is slipping only then when
relatively high forces are applied at the free cable ends. As a
result of the high strength of the ultrahigh molecular weight
polyolefin fibers, and ultrahigh molecular weight polyethylene
fibers in particular, such high tensioning forces can be sustained
by the cable without fracturing. The connection is preferably made
by tying a knot, although the skilled person may easily envisage
other types of such slipping connections. According to the
invention, after making the slipping connection, e.g. around two or
more bone parts, the two free ends of the knotted cable are pulled.
When the force applied is high enough, the knot will slip, thereby
tightening the cable around the bone parts. In this process, part
of the pulling energy brought into the cable ends will be
dissipated in the slipping connection. This means that the build up
tension in the cable ends will on the average be higher than the
average tension in the cable loop around the objects, in particular
the bone parts. Preferably, the average tension in the cable ends
will exceed the average tension in the cable loop by a factor of 4
to 5, in order to let the connection slip and tense the loop
further. Ultrahigh molecular weight polyolefin fibers, and
ultrahigh molecular weight polyethylene fibers in particular, have
sufficient strength to allow applying such high tensioning
forces.
[0008] In the method of the invention, the connection is made such
that the strength of the cable and the connection exceeds the
average tension required to allow the connection to slip, thereby
tightening the cable around the object and thus tying together the
objects, in particular fixing the bone parts. This will allow to
bring the cable under the required tension by pulling the cable
ends and letting the connection, or preferably the knot, slip. When
the required tension has been reached, the cable ends may be
released. In a preferred embodiment of the method, the average
tension in the cable around the objects, e.g. due to expansion of
the bone parts, is lower than the force which will allow the
connection to slip. In this way, the connection will not slip but
will actually sustain the tension in the cable around the bone
parts, at least for some time. A separate fixing device is in
principle not required therefore. The slip strength of the
connection depends on a number of factors, including for instance
the fibrous structure of the cable, the cable material properties,
and, in the preferred case of a knot, its construction. The skilled
person can easily adjust slip strength by mere experimentation.
[0009] Although the method according to the invention in principle
allows tying together objects, in particular fix bone parts, for a
prolonged time period, a preferred method includes the step of
locking the tensioned cable against the influence of forces acting
counter to the exerted force for some period, in case of an
operation at least for the post-operative period. Fixing of the
cable may be done by guiding the free ends from opposite sides
through holes in a metal block, and pinching the metal block such
that the holes collapse and fix the cable. Preferably locking the
tensioned cable against the influence of forces acting counter to
the exerted force is achieved by tying at least one additional knot
in the cable ends. The number of knots required depends on the
characteristics of each particular case. Additional knots may also
be used to adjust the slip strength of the slipping connection,
particularly when this connection comprises a knot.
[0010] According to the invention the surgical cable is laid around
at least part of the objects to be tied together, in particular the
bone parts to be fixed. Preferably, the surgical cable is laid
around the complete objects to be tied together by forming a loop
around the complete objects. Another option is to form a plurality
of loops, for example 2, 3 or even 4 or more loops with the
surgical cable around the objects to be tied together, in
particular the bone parts to be fixed. This offers the advantage of
a more secure connection.
[0011] Ultrahigh molecular weight polyolefin fibers are known per
se, and have an elongate body whose length dimension exceeds the
transverse dimensions of width and thickness. The term fibers
includes but is not limited to a filament, a multifilament yarn, a
tape, a strip, a thread, a staple fiber yarn, and other elongate
bodies having a regular or irregular cross-section. Preferably, the
ultrahigh molecular weight polyolefin fibers used in the cable have
a tensile strength of at least 1.2 GPa, preferably at least 1.8
GPa, and a tensile modulus of at least 40 GPa, preferably at least
60 GPa. Using steel cables for tying objects, and particularly bone
parts, together, brings about a number of disadvantages. They are
prone to fatigue, leading to fracture of the composing steel
fibers, the sharp ends of which stick out into the body. Fracture
of the fibers during their application by a surgeon entails the
risk of stitching and possible blood contact. Further, steel is a
hard material and therefore brings the risk of carving into the
bone when tensioned around it. The use of ultrahigh molecular
weight polyolefin fibers in the method of the invention does not
have these drawbacks, yet offers the desired strength level.
[0012] Homopolymers and copolymers of polyethylene and
polypropylene are particularly suitable polyolefins for the
production of the ultra-high molecular weight polyolefin fibers.
The polyolefins may contain small amounts of one or more other
polymers, in particular other alkene-1-polymers. A particularly
preferred polyolefin comprises ultrahigh molecular weight linear
polyethylene, having a weight average molecular weight of at least
400,000 g/mol, more preferably at least 1,000,000, most preferably
at least 2,000,000. In the context of this application, linear
polyethylene means a polyethylene having less than 1 side chain per
100 C atoms, preferably less than 1 side chain per 300 C atoms.
[0013] Preferably polyethylene fibers are used which comprise
polyethylene filaments, prepared by a gel spinning process. A
suitable gel spinning process is described in for example
GB-A-2042414, GB-A-2051667, EP 0205960 A and WO 01/73173 A1, and in
"Advanced Fiber Spinning Technology", Ed. T. Nakajima, Woodhead
Publ. Ltd (1994), ISBN 185573 182 7. In short, the gel spinning
process comprises preparing a solution of a polyolefin of high
intrinsic viscosity, spinning the solution into filaments at a
temperature above the dissolving temperature, cooling down the
filaments below the gelling temperature, thereby at least partly
gelling the filaments, and drawing the filaments before, during
and/or after at least partial removal of the solvent.
[0014] The method according to the invention may be used for tying
any objects together by tensioning a cable around the objects.
These fields of applications are less critical than the fixing of
bone parts however, and the advantages of the invention and the
preferred embodiments thereof in particular manifest themselves in
the fixing of bone parts. The method is also useful for connecting
bones to artificial elements providing some supporting function,
such as a splint for instance.
[0015] A particularly preferred cable is a bundle of parallel,
twisted or braided fibers of the type described above. The cable
may also comprise a tape having the required strength and modulus.
The tape may be a single tape or may be in the form of a flat braid
of ultrahigh molecular weight polyolefin fibers. Twisting and
braiding are commonly applied in cable production and cables
obtained by these techniques are applicable in the method according
to the invention. In constructing braids and twisted bundles, an
efficiency loss usually occurs, which means that the resulting
strength of the construction is lower then the average strength of
the constituting fibers. In the state of the art, the tension
forces in each separate cable required to fix bone parts generally
do not exceed 800 N. This is to prevent the cable from cutting
through soft bone or bone suffering from osteoporosis for instance,
or to prevent crushing of bone fragments. Also, when using steel
cables too high tension forces may cause fraying or fracture of the
cable. According to the invention, pulling forces on the free cable
ends, after making the knot, are preferably higher than 500 N, more
preferably higher than 750 N, even more preferably higher than 900
N, and most preferably higher than 1200 N. These are the preferred
pulling forces for a single leg. When pulling on a closed loop
using such a cable, which can be made by making a knot at the ends
of the two free legs, the preferred pulling forces are twice the
indicated values, i.e. 1000 N, 1500 N, 1800 N, and 2400 N,
respectively. The cable construction and method of connection
should be able to sustain such loads. The cable obviously must be
adapted to be positioned around the objects, in particular the bone
parts, to be fixed. In particular, its length should be sufficient
to be laid around the objects, to be tied together by applying a
slipping connection, and to be tensioned by pulling the free
ends.
[0016] In a preferred method according to the invention the force
exerted on the end parts of the cable yields a tensile stress in
the end parts of at least 650 MPa, more preferably at least 800
MPa, still more preferably at least 1000 MPa, and most preferably
at least 1200 MPa. The use of ultrahigh molecular weight
polyethylene fibres in particular allows to tension the cable at
such high stress levels.
[0017] A preferred embodiment of the method according to the
invention comprises releasing the tension after tensioning the
cable for the first time, adjusting the connection, preferably by
adding one or more knots, and subsequently applying a preferably
higher tension to the free legs, to allow the adjusted connection
to slip, thereby increasing compression force on the objects. More
preferably, after releasing the tension again, additional knots are
applied to increase knot security, and the legs are cut off at the
desired length. The advantage of this embodiment is that the level
of compression can easily be adjusted and the security of the
connection increased.
[0018] The ends of the cable may, when shaped as a bundle of
fibers, be treated to prevent unraveling or splitting of the
bundle. The ends may for instance be glued together with a suitable
substance, or they may be melted together or otherwise be prevented
from unraveling. A cable end may also be formed into an eye by
splicing the end back into the fiber bundle. In this case eyes form
the end parts of the cable.
[0019] According to the invention, the cable is preferably
positioned around the objects, in particular the bone parts,
following a trajectory that is stable when the cable is tensioned.
This prevents the cable from moving to a shorter trajectory,
leading to loss of tension in the cable and consequently loss of
fixing. Generally this will be the shortest trajectory at a certain
position along the objects or bone parts. Alternatively the cable
along the trajectory may be prevented from sliding to a shorter one
by natural obstacles as bone processes or artificial fixing devices
or protrusions applied to the bone parts.
[0020] In the method of the invention a slipping connection is made
in the cable, preferably by tying one or more knots. Suitable knots
for this purpose are in principle elementary simple knots. Examples
of suitable knots are a flat knot, a loop knot, a surgeon knot, a
water knot, a tape knot, a double figure eight knot and a double
overhand bend, or any combination thereof. These knots may also be
applied as additional knot, but preferably a two flat half or flat
overhand knots are used for this purpose. The person skilled in the
art may easily select other suitable knots, for example the
so-called double ring hitch, the Kellig hitch, or Prusik and
Klemheist knots. These and other knots, and methods to make them
can be found in the `Handbook of knots`, (Dorling Kindersley Book,
London 1998; ISBN 0751305367), and in "The Ashley book of knots`
(Faber and Faber Ltd, London 1990; ISBN 057109659x).
[0021] After the slipping connection has been made in the cable,
the cable ends are pulled with a certain tensile force to tighten
the cable loop around the objects, in particular the bone parts.
Preferably a tensioning device is used for this purpose, which will
be described below. In all embodiments disclosed the tensioning
action is continued until the required tension in the cable is
achieved. Subsequently, the tensioned cable must be locked against
the influence of forces acting counter to the exerted force.
[0022] The invention also relates to a tensioning device for a
surgical cable. The tensioning device is to be used in conjunction
with the above described method. Known tensioning devices cannot be
used since the forces required to tension the cable by far exceed
their load bearing capacity. In US 2004/0127907 at p. 3, [0051] it
is said that tension force in cable normally is between about 5 to
about 800 N. If the tension force in the cable is too high,
damaging of the objects to be tied together may take place. For
that reason the known devices are designed to be restricted to that
tension. Because devices are manually operable it is not possible
to apply the high tension, also devices would not be stiff and/or
strong enough to sustain the required tension levels. Some devices
even have special mechanisms to put an upper limit to the tension
that may be applied in the cable. In the method according to the
invention however the level of tension force at the ends of the
cable may exceed 900 N, preferably exceeds 1200 N, more preferably
exceeds 1400 N, even more preferably exceeds 1600 N and most
preferably exceeds 2000 N. These tension levels preferably apply in
case of a braid construction made of Dyneema Purity.RTM. or Spectra
with a diameter of between 0.7 and 1.4 mm. In case a closed loop
made of the same cable is tensioned, by placing a non-slipping knot
at the end of the two legs, the tensioning device should be able to
support tension levels exceeding at least 1000 N, more preferably
exceeding 1500 N, even more preferably exceeding 1800 N, and most
preferably exceeding 2400 N. The tensioning device according to the
invention comprises a restraining body adapted to restrain the
surgical cable to be laid around at least part of the objects to be
tied together, and an adjusting mechanism adapted to cooperate with
the restraining body to change the tensile force applied to the
surgical cable, with the proviso that the device is adapted to
allow the surgical cable to be tensioned by the restraining body at
a tension of at least 900 N. Preferably the tensioning device is
adapted to allow the surgical cable to be tensioned by the
restraining body at a tension of at least 900 N, even more
preferably at least 1200 N, even more preferably at least 1500 N,
still more preferably at least 1800 N and most preferably at least
2400 N.
[0023] The device is adapted to allow the cable to be tensioned,
means that the apparatus will not be damaged, like breaking or
bending, or that no restrictions are in the apparatus to raise the
level of tension force. Preferably the device is operated by a an
electrical motor.
[0024] The tensioning device is adapted for holding the end parts
of the cable. In case a cable having end parts in the form of an
eye is applied the device may comprise two hooks or similar that
each can hook to one of the eyes of the cable and be provided with
means to draw the hooks to one another. Such means can comprise a
mechanism as used in turn buckle, a worm wheel and driving screw
combination or two cooperating 45 [deg.] tooth wheels rotating
around mutually perpendicular axes. These tensioning devices can be
connected to the cable in such a way that only a drawing force is
exerted on the cable, resulting in its shortening and tensioning
but also in such a way that, instead of or next to the drawing
force, also a twisting force is exerted on the cable, also
resulting in further tensioning the cable.
[0025] A preferred embodiment of the tensioning device according to
the invention has a restraining body comprising an adjustable
frame, provided with at least two guiding means in opposite corners
of the frame, between which means a surgical cable can be
tightened, the adjusting mechanism being adapted to change the
relative distance between said corners of the frame. The adjusting
mechanism may be mechanical, in which case it preferably comprises
a rotatable member, such as a screw. Such a device is easily
manipulated, and allows to adjust the average tension in the cable
ends with the precision required. Another preferred adjusting
mechanism comprises a hydraulic pump.
[0026] In order to be able to preset a certain tension in the cable
the tensioning device is preferably equipped with measuring means
for the applied tension. Such means are known per se and any known
means to measure forces may be used.
[0027] The invention will now be further explained by the following
figures, without however being limited thereto. Herein:
[0028] FIG. 1 schematically represents a tensioning device
according to the invention; and
[0029] FIG. 2 schematically represents a possible sequence of steps
of the method according to the invention.
[0030] With reference to FIG. 2, in the method according to the
invention a surgical cable 10, is laid around bone parts 40 in
order to fix them (FIG. 2A). Bone parts 40 may for instance
comprise a cut bone piece, e.g. a sternum for the purpose of an
open-heart surgery. Surgical cable 10 consists of a braid of
ultrahigh molecular weight polyethylene fibers (Dyneema.RTM. SK75
yarn, 1760 dTex). Cable 10 has two end parts 11 and 12, which may
consist of single cable, but which may also be formed by folded
back portions of cable 10, forming a loop. A first surgical cable
10 is laid around or through the bone parts 40 (FIG. 2A), for
instance using a needle, and a first slipping connection in the
form of a knot 14 is placed in this cable by bringing the two end
parts (11, 12) together and tying them (FIG. 2B). As shown in FIG.
2C, the remaining legs (11, 12) from the first knot 14 are then
positioned around a tensioning device 1, in this case each with an
additional loop around the tensioning device and tightly fixed with
a non-slipping knot 15, for instance by hand-force. A tensioning
force F1 is then applied to increase compression onto the bone
pieces 40. The manner in which the tensioning force may be applied
by the tensioning device 1 is described further below.
[0031] According to the invention the force F1 exerted on the end
parts (11, 12) exceeds the force to allow slip of the knot (14),
using a tensioning device 1, which is able to sustain an average
tension in the cable of at least 500 N, without substantial loss of
tension. With the phrase "without substantial loss of tension" is
meant that the tensioning device 1 is dimensioned such that the
tension in cable 10 remains substantially equal to the required
(preset) tension, at least during the process of tying together the
objects, in particular the bone parts 40. In this process of
tightening, the build up tension in the cable ends (11, 12) will on
average be higher than the average tension in the cable loop 16
around bone parts 40. According to a preferred embodiment, the
tensioning force is then released, the legs (11, 12) are cut off
just under the non-slipping knot 15 and the tensioning device 1 is
then removed, as shown in FIG. 2D. Enough length in both legs (11,
12) will be available thereafter, if they are positioned around the
tensioning device with an additional loop. After having tightened
the cable loop 16 around bone parts 40, the tensioned cable is
locked against the influence of forces acting counter to the
exerted force by tying at least one additional knot 17, for
instance by hand-force.
[0032] A second cable 10 may then be positioned around or through
the bone parts 40, e.g. using a needle, and a first slipping knot
14 in this cable is placed. Again, the remaining legs (11, 12) from
the first knot 14 in this second cable 10 are positioned around the
tensioning device 1, again with an additional loop, and tightly
fixed with a non-slipping knot 15, for instance by hand-force. A
tensioning force F2 is then applied to increase compression onto
the bone pieces 40 (see FIG. 2E). Positioning of the second cable
(and further cables) may influence the tension in the first cable
(and other previously applied cables). For instance the tension in
the first cable may drop when the second cable is applied. When
this is undesirable, the first cable may be tensioned further after
having applied the second cable in order to increase its tension to
the desired level. Preferably, a fixating device is then
temporarily used. It is also possible to initially overstress the
first cable, whereby the tension in the first cable will drop to
the desired level upon applying the second cable.
[0033] Referring to FIG. 2F, in the embodiment shown, a total
number of 4 cables are applied using this approach to fix the bone
pieces 40. During the tensioning procedure bone parts 40 will
gradually come closer to each other (compare to FIG. 2B for
instance). The applied tensioning forces F1, F2, F3 may be equal to
each other. It is also possible that they mutually differ, for
instance that F1>F2>F3.
[0034] After the 4 cables have been tensioned and a second knot has
been placed for each cable, a possible second tensioning procedure
can be added, as demonstrated in FIG. 2G. A similar approach as in
FIG. 2C is used, although it may not be possible to apply an
additional loop around the tensioning device due to the limited
length of both legs due to the first tensioning procedure. The
remaining legs from the second knot in this cable are thus
positioned around a tensioning device 1 and tightly fixed with a
non-slipping knot, for instance by hand-force. A tensioning force
T1 is then applied to increase compression onto the bone parts
40.
[0035] As shown in FIG. 2H, the bone parts may touch during the
tensioning procedure and will be compressed (compare to FIG. 2G).
The tensioning force is released and the tensioning device has been
removed. By cutting off the legs just under the non-slipping knot,
enough length in both legs will be available to apply final
additional knots in this cable, for post-operative security
reasons, tightly fixed by hand-force for instance.
[0036] As shown in FIG. 2I, the second cable with the additional
knot will be tensioned using a similar approach as shown in FIGS.
2G and 2H, including the additional knot for post-operative
security.
[0037] Finally, as shown in FIG. 2J, all cables will be tensioned
using the approach of FIGS. 2G and 2H, and the bone parts will
obtain the preferred compression and additional knots may be added
for post-operative security.
[0038] With reference to FIG. 1 a tensioning device 1 is shown
which is preferably used in connection with the above described
method, in which a surgical cable 10 is laid around bone parts 40,
and provided with a slipping connection (14, 15). The device
comprises a restraining body 20 adapted to restrain a portion of
the surgical cable 10. Restraining body 20 comprises an adjustable
frame 21, consisting of 4 frame members 21a, 21b, 21c, and 21d,
Frame members 21a to 21d are mutually connected through 4 pivots A,
B, C and D. Frame 21 is further provided with two guiding means
(22, 23) in opposite corners A and C of frame 21, between which a
surgical cable 10 can be tightened, e.g. by using a non-slipping
knot 16 around guiding means 22. Tensioning device 1 is further
equipped with an adjusting mechanism 30 being adapted to change the
relative distance between corners A and C of frame 1. As shown in
FIG. 1, a simple arrangement consists of a rotating screw 31 and
handle 32. Other arrangements, such as a hydraulic pump, may also
be used. By turning the handle 32 in direction R, the screw will
rotate and alter the distance between corners B and D. Since frame
members 21a to 21d are stiff, this process also alters the distance
between corners A and C. For instance the distance between pivots A
and C can be increased by decreasing the distance between pivots B
and D. Such an increase of the distance between A and C actually
brings the cable 10 under increased tension. Essential to the
invention is that the tensioning device is adapted such that it can
sustain an average tension in the cable of at least 1000 N, since
the tension is applied on both legs, without substantial loss of
tension, in particular in case a braid construction made of Dyneema
Purity.RTM. or Spectra with a diameter of between 0.7 and 1.4 mm is
used. In order to monitor the average tension in cable 10,
tensioning device 1 is equipped with measuring means 33 for the
applied tension. Any suitable means known in the art to measure
forces may be used as such. When used for tensioning a surgical
cable tensioning device 1 should be made of material that is easily
cleanable, and that can be readily sterilized.
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